The present invention relates to a steering apparatus for a vehicle in which an axle supporting arm is vertically swingably supported by a vehicle body, the axle supporting arm extends forward from the vehicle body, and a front axle is fixed to a front end of the axle supporting arm.
FIG. 8 shows a conventional two-wheeled motor vehicle, i.e. a motor cycle (JP 2011-941 A) having a front wheel supporting structure of a swing arm manner. A front axle 202 integrally provided with a kingpin (not shown) is fixed to a front end of a swing arm 201, a knuckle 203 is mounted on the kingpin such that the knuckle 203 can laterally be steered, and a hub 205a of a front wheel 205 is rotatably supported by the knuckle 203.
A pair of left and right knuckle arms 203a projecting upward is rigidly fixed to the knuckle 203. Upper ends of both the knuckle arms 203a are integrally coupled to each other. A laterally extending steering arm 212 is coupled to a lower end of a steering shaft 211 which is turnably supported by the head pipe 210. Both left and right ends of the steering arm 212 and the pair of left and right knuckle arms 203a are laterally turnably connected to each other through a pair of left and right link arms 213.
As another conventional technique, there exists a steering apparatus for a two-wheeled motor vehicle in which a pair of left and right upwardly extending fork members supports a front axle, and the fork members are connected to a steering shaft through a link mechanism (JP 2011-201335 A).
According to the conventional structure shown in FIG. 8, the knuckle arms 203a and the link arms 213 which are utilized for steering configure, together with the swing arm 201, a parallel link mechanism which vertically swingably supports the front axle 202 and the front wheel 205. Therefore, when the front wheel 205 vertically swings, since a reaction force from a road surface is shared and received, the link arms 213 and the knuckle arms 203a are required to have rigidity of a certain level or higher. Hence, a weight of the steering apparatus increases, and a great steering force is required at the time of steering. Further, a structure of the steering apparatus also becomes complicated.
In the latter conventional technique, when the vehicle laterally swings, a large front frame and large handlebars which support the front axle also laterally swing, and a great steering force is required.